Pigmented paper and preparation



July 5, 1960 L. B. TAYLOR PIGMENTED PAPERAND PREPARATIONTHEREOF OriginalFiled Oct. 31, 1955 in ilml mi lDVdO .LNSD '33:! HEN 3 INVENTOR.

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.LNBD lid AJJDVdO United States Patent PIGMENTED PAPER AND PREPARATIONTHEREOF Continuation of application Ser. No. 543,835, Oct-31, 1955. Thisapplication July 31, 1959, Ser. No.

13 Claims. (Cl. 162-181) The present invention deals with pigmentedpaper and the manufacture thereof, and more particularly involvesenhancing the opacity, brightness and other desirable properties ofpaper by pigmentation with titanium dioxide and finely divided,amorphous siliceous materials.

Heretofore, various proposals have been otfered for improving paperquality, especially with printing papers, by pigmentation withmaterials, one T of the most noteworthy ofv which is titanium dioxide.Due to its high cost, titanium dioxide is not economically suitable forall grades of paper but finds favor in only the more expensive papers.Also, the retention of titanium dioxide in paper during the papersheeting step leaves room for betterment. Among other things, therecovery and recirculation of unretained titanium dioxide in the whitewaters is cumbersome and inelficient.

According to the present invention, the disadvantage and high costswhich accompany titanium dioxide pigmentation are minimized and/orobviated. It is possible to reduce the required quantity of titaniumdioxide, and consequently the cost of pigmentation, while notsacrificing paper quality. Instead, paper of improved opacity andbrightness is obtained. Further realized is increased pigment retentionin the paper sheeting step.

Now it has been discovered that such benefits ensue from sheeting a pulpslurry which includes both titanium dioxide and a finely divided,amorphous siliceous pigmentary material, notably calcium silicate.Viewed otherwise, it has been found that up to 90 weight percent oftitanium dioxide normally required for a given pigmentation may bereplaced with finely divided, amorphous siliceous pigments of much lesscost. As a consequence, costs are reduced and a pigmented paper isprepared which has high opacity, brightness and increased quantities ofpigment. Often these paper qualities are superior to those which can beobtained using either titanium dioxide or the siliceous materialindividually.

Figures I and II in the drawing pictorially demonstate the synergisticeffects observed in connection with the practice of this invention.Thus, in Figure I, the variations in opacity and ash (pigment retainedin the paper) for difiering ratios of titanium dioxide and calciumsilicate are graphically shown. With only titanium dioxide the papersopacity is about 86.5, yet opacities in excess of this value areachieved with pigmenting materials containing from about 40 percent toabout 95 percent titanium dioxide by weight of titanium dioxideandcalcium silicate. Furthermore, even with larger percentages of calciumsilicate opacities are of values which are in excess of those whichmight be expected from the contribution thereto of the respectivepigments.

In a similar fashion, greatly increased ash contents are observedby'practice of this invention. For the given conditions, hereinafterdetailed, ashes are of'about 6.5 percent with either pigment, yet whenusing combinations thereof, ashes range substantially above 6.5 percentand as high as about 8.3 percent (when the pigment comprises 80 72,943,911 Patented July 5, 1960.

ice

percent titanium dioxide by weight thereof and calcium silicate).

Thus, according to one embodiment, the utilization of calcium silicateor comparable pigmentary siliceous material oifers an expedient forincreasing the concentration of pigment composition including titaniumdioxide in paper. In another embodiment, paper opacities in excess ofthose possible with titanium dioxide are realized. And in a stillfurther embodiment, the value of calcium silicate or other siliceousmaterial, particularly those of low cost, may be increased as anopacifying agent. In practice, the advantages of the present inventionare realized by recourse to any of a number of procedures. Briefly, bothtitanium dioxide and the siliceous ingredient, notably finely dividedcalcium silicate, are added to a pulp slurry most advantageously afterthe pulp has been beaten suitably following usual paper beatingpractices. Thereafter, the slurry pH is adjusted to within the range ofabout 4 to 6.5, notably pH 5, by adding an acidic material such asaluminum sulphate or other sulphuric acid salt including sodium sulphateand sodium bisulphate or sulphuric acid itself. Also, other acidicmaterials, generally inorganic acids such as hydrochloric acid, carbonicacid, etc. or their anhydrides or acid salts are etfective. Aluminumsulphate (alum) finds widest use, not only because it is particularlyeffective but also because it is a common material used in papermanufacture for other reasons. Because of its low cost, sulphuric acidis an excellent replacement for part or all of the alum. This acidifiedslurry is sheeted into paper on recognized apparatus, e.g. a Fourdrinieror cylinder machine.

Sometimes, after including the pigments in the pulp slurry, evenfollowing substantial beating, the dispersion of the pigments isenhanced by further agitation of the pulp slurry as by mechanicalstirring or even beating. This facilitates uniform distribution of thepigment throughout the slurry. i

Depending to some extent upon the exact paper employed, the particularquality of paper desired, and other peculiarities of any given paperforming operation, the ratio of the two pigments may be varied.Beneficial results are obtained when employing from about 10 to aboutpercent titanium dioxide by weight of titanium dioxide and calciumsilicate. With lower titanium dioxide concentrations, the pigmentingqualities of calcium silicate are upgraded strikingly and according toone em-' bodiment hereof, this constitutes an important consideration inutilizing the concepts of this invention. Thus, when papers of opacitiesslightly higher than are otherwise attained with calcium silicate orcomparable siliceous material are the object, a minor quantity oftitanium dioxide sufiices.

However, in a preferred embodiment, the titanium dioxide is employed inquantities ranging from about 35 or 40 percent to about 95 percent byweight thereof and calcium silicate. Opacities exceeding those oftitanium dioxide pigmented papers are realized within this range, seeFigure I of the drawing and Example I hereinafter.

With certain pulps, the contribution to'opacity and other papercharacteristics by both the combination of titanium dioxide and calciumsilicate appears even more noticeable, note Example II hereinafter andFigure II of the drawings. There, paperprepared from a pulp fumishconsisting solely of kraft pulp to which had been added both pigmentarymaterials was of superior opacity and brightness by comparison with thevalues obtained with the individual pigments regardless of the ratio ofthe titanium dioxide and calcium silicate.

Mixtures of titanium dioxide and calcium silicate, for this invention,may be provided directly in the pulp slurry by addition of requisitequantities ofindepeudently prerior-to being added to the slurry.

In the case of siliceous materials, such as the preferred calciumsilcate, the pH adjustment of the slurry may include a chemical change.Aluminum sulphate reacts with calcium silicate, probably to providea'calcium aluminum silicate and calcium sulphate, the latter having somewater solubility whichmay, at least in part, account for removal ofcalcium sulphate-in the white waters. Chemical reactions may beencountered with other silicates, notably between alkaline earth metalsilicates, and othenuseful acidic materials which form water insolublealkaline. earthmetal salts. For the most part, the acidic materialrequirements for pH adjustment are less-than the stoichiometric quantityneeded to react completely with "the siliceous pigment. Hence, usuallyat least a portion or silceous pigment such ascalcium silicate reactswiththe acidic material, e.g. aluminum sulphate. Under specializedcircumstances the calcium silicate may be completely reacted ordecomposed. In many instances, the reaction between the acidic materialand siliceous pigment proceeds so slowly that the acidic material is notcompletely consumed prior to sheeting.

A large variety of finely divided, amorphous pigmentary siliceousmaterials containing at leastabout 50 percent SiO byweight (anhydrous orwater free basis)-are useful either alone or in combination. Foremostamong these are the finely divided, amorphous, pigmentary calciumsilicates ranging in surface areasfrorn to 60 square meters per gram, asmeasured by theBrunauer-Emmett- Teller method described in the Journalof American Chemical Society, volume 60, page 309 (1938) whichcorresponds to the formula CaO(Si0 x ranging from about 2 to 5, andparticularly from 2.9 to 3.8. Those calciumsilcates having packed bulkdensities prefer-ably from 0.1 to 0.4 gram per cubic centimeter asmeasured at three pounds per square inch give pronounced benc- Boundwater is the difierence between the free water and that water which isremoved by heating at ignition temperatures, e.g. 1000 to 1200" C. Itappears the bound water is chemically united, whereas the free water ismore loosely contained by, the siliceous material.

I The titanium dioxide component is comprised of the usual paper-pigmentquality titanium dioxide, e .-g. a'finely divided, particulate materialhaving particles on the average of 0.3 micron diameter. Other grades ofpigmenting titanium 'dioxid'e inay find utility, especially in view. ofthe beneficiating effect of the siliceous material.

The following examples illustrate the manner in which this invention maybe practiced:

' EXAMPLE 1 p A pulp'beatei was "charged with 2 50 grams of kraft pulpand 25-0 grams of sulfite pulp, dispersed in 23 liters of water andbeaten in a Niagara beater to a freeness of 550'millilit'ers (Canadianstandard). To this beaten pulp was added 400 cubic centimeters ofaqeuous slurry containing 35 grams of pigment comprised of titanium dioxide and/or calcium silicate, as indicated in Table I, followed bymixing for five minutes. A smallquantity of aluminuin sulphateoctadecahydrate, as indicated in Table I, was added adjusting the slurryPH at 5.0. The resulting acidic slurry was then sheeted on a laboratoryNoble-Wood sheeting machine and the opacity, brightness and ash, contentof the paper determined.

ficating effects. Such calcium silicates appear to be in the form offiocs of finely divided ultimate calcium silicateparticles when viewedunder high magnification.

Under the electron microscope, the flocs resemble clusters of grapes andappear to be a loosely connected agglomeration of ultimate particles.Their ultimate particle size is below' 1.0 micron, usually in the rangeof 0.015 to 0.2 with the average particle size being from 0.04 to 0.08micron. The flocs range in size from about 0.6 or 1 mimom to as high as10 microns, the majority thereof, e.g. at least about 55 per cent byweight, being from 1 to 5 microns. I

The beneficial effects are not limited to use of the preferred calciumsilicates, but may be obtained by recourse to other finely divided,amorphous siliceous materials. Somewhat finer calcium silicates whichhave BET surface areas ranging upwards of 50 or 60 to from 120 to 200square meters per gram comprise a useful component. Still otheramorphous, finely'divided calcium silicates and mixed calcium silicatescontaining at least about 50 weight percent SiO and of below 1.0 micronparticle size, more preferably below 0.3 micron, are included. Among.these'are calcium aluminum silicate, calcium sodium silicate, potassium"silicate, aluminum silicate,'calcum zinc silicate, andthe like.strontium silicates. and barium silicates possessing the aboveenumerated physical and chemical characteristics are likewise ofutility.

Finely divided, amorphous, precipitated pigmentary silica can beemployed. Usually these, silicas are of from 20 to 120 square meters pergram BET surface area and have ultimate particle sizes on the order ofthose of the described calcium silicates, e.g. below 1.0 micronandnotably less than 0.3 micron. They too are composed of fiocs of ultimateparticles. I

The preferred siliceous materials contain both bound water and freewater. Free water is that water which isxremoved .byheating for 24 hoursat 105 C.

Magnesium silicates,

The titanium dioxide charged comprised paper grade materialand had anaverage particle size of 0.3 micron. The calcium silicate used had aBE-T surface area of '31 square meters per grain, and an averageultimate particle size or 0.04 to 0.08, with particles ranging from0.015 to 0.20'micron. By chemical analysis it was comprised of 66.4percent SiO 18.6 percent CaO, 0.39 percent Na and 0.60 percent chlorine.In aqueous slurry it had a pH of 10.6. Upon heating at ignitiontemperature 1000 (1., it lost 15.1 percent by weight, and upon heatingat 105 C. iii a laboratory drier for 24 hours it lost 5.2 percent byweight, indicating a free water content of 5.2 percent and a bound watercontent of 9.9 percent by weight.

Table I lists the various reaction variables along with the propertiesof the prepared paper.

Table I Loading-Weight, Percent Paper Properties Calcium Ash Opacity,Bright- Silieate T10, Alum Weight Percent ness,

Percent Percent 0 10 0. 3' 6. s7 86. 4 s5. 9 2 8 1. 7 8.31 88. 5 86. 7 45 3. 1 7:95 83. 1 86. 7 6 .4 4. 6 7. 5D 86. 9 85. 7 8 2 6. O 6. 85 34. 684. .7 10 0 7. 5 6. 60 81. 4 82:2

Total pigment'loadin'g is 10 percent by weight. I Weight percent, based.on dry pulp, of AMS O0z.18H,O.

Figure l of the drawings graphically correlates milliliters freenesspaper wasprepared. Table 11, here after, lists the experimentalvariables and properties of the resulting papers.-

v 1 Total pigment loading is 10 percent by weight.

. Welght percent; based on dry pulp, of A1:(S0:)4.18H|O.

Figure 2 of the drawings graphically shows the variationsfin-paperopacity. observed as the pigment components were varied. It.will benotedthat whenever the pigment comprised both titanium dioxide and calciumsilicate,the paper opacity exceededthe opacity of paper pigmentedindividually withcach component. A substantial improvement inopacityisYobserved over a wide rangeof mixtures. A

EXAMPLE III A pulp beater was charged as follows:

I Y j Grams Unbleached sulfite pulp 90 Bleached kraft pulp 180 Hardwhite envelope cuttings 90 This charge was dispersed in 23 liters ofwater and the resulting slurry was beaten in a Niagara heater for about80 minutes to approximately 400 .milliliters freeness, Canadian standard(TAPPI Standard T227 111 50). One

hundred milliliters of prepared rosin of about 5 percent by weightsize'was then added. Thereafter, 9 grams of pregelatinized starch wasadded and, the pulp was circulated in the beater long enough to insurecomplete mixing. Aluminum sulphate in the amount of 3 percent by weight,based on the dry weight of pulp, was added as a solution containing12.92 grams of aluminum sulphate octadecahydrate per liter. At thisstage, the pulp consistency was approximately 1.1 percent. Stirring wascontinued for 2 minutes. Immediately thereafter, the amounts of calciumsilicate having the composition CaO(SiO and titanium dioxide indicatedin the table were added. The amounts are expressed as percentages ofthedry Weight of the pulp. Stirring of the mixture was continued for 10minutes more, and the resulting stock was diluted to 8,000 milliliters,divided into ten 800-milliliter portions, and sheeted into paper. Thepaper was tested for brightness, opacity, bursting strength, weight andthickness, and ash and moisture content, with the following results:

Table III Percent titanium dioxide by weight Percent calcium silicate byweight Brightness:

Green li ht Blue light Contrast ratio (green light):

Reflectance, black backing lRtegectance, white backing Contrast ratio(blue light):

Reflectance, black backing Reflectance, white backing Ratio- Burstingstrength, lb./ln

Percent ash in oven dry paper oremq new around: rah-c: we on:-

prior paper making operations can be included. From 3 to 6 percent byweight of the slurry is pulp (dry basis) in accordance with normaloperations.

Suificient pigments are added to constitute from 0.5 to 30 percent byweight of the pulp on a dry basis. Ash values of the paper, by virtue ofthe high pigment retention obtained hereby, range from about 50 to 80 or90 percent of the pigment concentration in the slurry on a dry pulpbasis. I

In practicing paper pigmentation according 'to this invention, otherpaper making operations may be included. Sized or unsized paper can beprepared. For sized paper, a rosin size such as asoluble alkali metalrosin soap, e.g. sodium rcsinate or other typical size is included inthe pulp slurry and precipitated by use of a trivalent or tetravalentmetal such as titanic sulphate or aluminum sulphate.

Coloring matter, if desired, man be included in th pulp slurry duringthe beating cycle. Also, the pulp may be bleached by treatment withchlorine in an oxidizing form or with other bleaching agents.

Subsequent to sheet formation, the sheet is suitably dried and, whennecessary, calendered. Coatings may be applied to the sheet in thepreparation of high grade printing papers of the type used in moreexpensive magazines. A typical coating agent is finely divided clay.

This application is a continuation of application Serial No. 543,835,filed October 31, 1955, now abandoned, which is a continuation-in-partof prior applications Serial Nos. 352,295 now abandoned, and 393,522,filed respectively on April 30, 1953. andNovember 20, 1953. 1

Although the present invention is described with ref-.-

erence to particular details of special'embodiments, it is not intendedthat it .be limited thereto except insofar as the invention is definedin the claims. Y I Iclaim:

1. The method of preparing paper of enhanced opacity which comprises-adding titanium dioxide and a floccu lent finely divided, pigmentary,amorphous, precipitated siliceous material having an average ultimateparticle size below 1.0 micron in an aqueous paper pulp slurry,adjusting the pH of such slurry to between 4 and 6.5 by inclusion in theaqueous pulp slurry of an acidic material prior to sheeting and sheetingthe slurry.

2. The method of preparing paper of enhanced opacity which comprisesadding titanium dioxide and a flocculent finedly divided, pigmentary,amorphous, precipitated alkaline earth metal silicate having an averageultimate particle size below 1.0 micron in an aqueous pulp slurry,adjusting the pH of said slurry to between 4 and 6.5 by inclusion in theaqueous pulp slurry prior to sheeting an acidic material which forms awater insoluble alkaline earth metal salt and sheeting the slurry.

3. The method of preparing paper of enhanced opacity which comprisesadding titanium dioxide and a flocculent finely divided, pigmentary,amorphous, precipitated calcium silicate having an average ultimateparticle size below 1.0 micron in an aqueous pulp slurry, adjusting thepH of said slurry to between 4 and 6.5 by inclusion in the aqueous pulpslurry prior to sheeting an acidic material which forms a waterinsoluble calcium salt and sheeting the slurry. I

4. The method of preparing paper of enhanced opacity which comprisesadding titanium dioxide and fiocculent' finely divided, pigmentary,amorphous, precipitated calcium silicate having an average ultimateparticle size below 1.0 micron in an aqueous pulp slurry, adjusting thepH of such slurry to between 4 and 6.5 by inclusion in the aqueous pulpslurry of aluminum sulphate prior to sheeting, and sheeting the slurry.

'5. The method of claim 4 wherein the calcium silicate corresponds tothe formula, CaO(SiO,) x ranging from 2 to 5.

6. The method of claim 4 wherein the calcium silicate corresponds to theformula, CaO(SiO x ranging from particle'sizebelo'vv 1".0 micron andcontaining at: least 7 50 percent SiO by weight. a

*8. Pigmente'd-fcellulosic paperof enhanced opacity -c'ontainiri'gindependently prep'ared titanium dioxide and fa floccnle rit-finelydivided, ipigmentary, amorphous, precipitated siliceous -'material''having an'avera'g'e ultimate particle 'size below 1.0 micron and ofgatleast 50 percent 7 Sit): eentem by -vveigh't, the; tit'aniiim dioxideconstituting 'froi'ni 10 m 95 erCnfbYWEight thereofand the siliceousmaterial. e s

p 9. 'Pigine "ted cellulosic paper of enhanced opacity conspasm 7ttaming'mdepenqenuyg reparea titanium dioxide and a H succulent finelydivided', pigrnenta1 y, amorphous, precipitated siliceous materialhaying 'an'average ultimate particle size belovvyltdmicron and "of atleast 50 'p'ereent SiO content by weight, the titaniumdioxideconstituting firom 35th 95 percent by Weight thereof and the siliceousmate- I I a 10,; Pigmented cellulosic paper of enhanced opacity 'asopacity enhancing components flocculent amorphous, precipitatedsiliceous pigavmgan average ultimate particle size of dioxidejconstitiiting rromss't 'Qs percent by weight of the titanium dioxide and saidsiliceous material, the

remaining-at least 50 percent SiO b'y we 3O crop and titanium dioxide,said titanium V opacity of' said paper being :"gr'eater than that ofpaper 0 containing as its opacity "enhancing component titanium dioxidean amonnt equal to that of the siliceous material'andjtitanium dioxidein the paper.

11. A paper pigment composition effective in enhancing the opacity ofoellulosic paper-containing as opacity enhancing components flocculentfinely divided, amorphous, precipitated siliceous pigmentarymaterial'containing at least percent SiQ by weight and having an averageultimate par'ticiefsize of less than '1 micron and umtd ox desaid an umdiox desqnstitu ins 10 to a percent by weight of the titanium dioxideand siliceous material.

12. :A paper pigment composition effective in'enhancing the opacity ofcellulosicpaper containing as opacity enhancing components independentlyprepared, flocculent finely divided amorphous, precipitated "siliceouspigmentary material containig at least '50 percentfSiO, by weight andhaving average ultimate particle of thfan m 'mn an t di xid tt e' o ns un 35.3 4 95.1

pa of ephap i th greater degree than the fs amount of. titanium dioxideWithout h l ic ousr' atena r 13. A paper pigment composition enhancingthe opacity of cellulosic paper containing as opacityenhancingcomponents fldcculent :finely divided precipitatedsiliceous pigmentary,material containing at least 50 percent SiO: by weight and'havin'g anaverage ultimate particle size of less than 0.3 micron ancl titaniumdioxide, said titanium dioxide constituting 351:; 9,5 percent'by weight:the titanium dioxide andsiliceou's material.

References Cited in the file of this patent STATES P TENTS 2,000,031Lat-song--- a 1, 1935 237 :2 9 June 12, 1945 2,739,068 I Eichmeier Mar.20, 19.56 2,786,757 Taylor L-.. Mar. 26 1957 Allen Mar. 26, 1957 j t mumI ercent hy weight of the. titanium dioxide and 's'iliceousmaterial;pigmentgbeing v UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTIONPatent Nor-2,943,971 July 5, 1960 Louis B. Taylor R It is herebycertified that error appears in the above numbered patent requiringcorrection and that the said Letters Patent should read as correctedbelow'.

Column 8 lines 37 and 38, for "-beneficating" read beneficiating column5, Table III first column line 14 thereof for "Bursting strength, lb./inread Bursting 2 strength lb./ in. column 6, line 4L? for "finedly" readfinely column 8, line 14, for "containig" read containing I Signed andsealed this 25th day of July 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

7. PIGMENTED CELLULOISE PAPER OF ENCHANCED OPACITY PIGMENTED WITHINDEPENDENTLY PREPARED TITANUIM DIOXIDE AND A FLOCCULENT FINELY DIVIDED,PIGMENTARY, AMORPHOUS, PRECIPATED SILICEOUS MATERIAL HAVING AN AVERAGEULTIMATE PARTICLE SIZE BELOW 1.0 MICRON AND CONTAINING AT LEAST 50PERCENT SIO2 BY WEIGHT.